Signicance of Experimental Data in the Design

Journal of Wuhan University of Technology-Mater. Sci. Ed. Feb.2014 131

Signi cance of Experimental Data in the Design of Structures Made from 1.4057 Steel

Brnic J1 , Turkalj G1, NIU Jitai2,3, Canadija M1, Lanc D1(1.Department of Engineering Mechanics, Faculty of Engineering, University of Rijeka, Vukovarska 58, 51000 Rijeka, Croatia2.School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China; 3.School of Materials Science and Engineering,

Henan Polytechnic University, Jiaozuo 454160, China)

Abstract: This paper presents experimentally-obtained data which can be of importance in the design procedure of engineering components made of 1.4057 (X17CrNi16-2; AISI 431) steel. In this manner, uniaxialy tests related to determine material mechanical properties and short-time creep behavior were performed. Based on the mentioned tests, ultimate tensile strength, 0.2 offset yield strength and modulus of elasticity at low and elevated temperatures were determined. Also, creep behavior of considered steel was tested for selected temperatures and selected stress levels. According to experimentally determined Charpy impact energy an assessment of fracture toughness was made.

Key words: material properties; short-time creep; fracture toughness calculation; 1.4057 steel

Wuhan University of Technology and SpringerVerlag Berlin Heidelberg 2014(Received: Feb. 19, 2013; Accepted: Dec. 23, 2013)

Brnic J: Prof.; Ph D; E-mail: [email protected]

DOI 10.1007/s11595-014-0880-0

1 Introduction

Failure in structures is a well-known technical problem. Different mechanical failure modes can be observed in all fields of engineering and may be numbered as: force or temperature induced deformation, yielding, fatigue, corrosion, wear, impact, creep, etc. Certain failure modes (corrosion, fatigue) are single phenomena, whereas others (corrosion-fatigue) are combined phenomena. The material properties of steel are linked to chemical composition, processing path, etc. The designer has to know which properties are required for a structure under consideration[1]. It is well known that a certain structure is intended to serve a defined aim at prescribed environmental conditions which may vary from low temperature conditions to elevated temperatures. At room temperature and in the absence of adverse effects, a properly designed structure will support its static design load for an unlimited time[2]. A sustained load of a certain level at elevated temperatures may produce inelastic strain in the material that increases with time. This phenomenon is known as creep[3]. An established de nition of creep

is that this is time-dependent behavior during which deformation continues to increase while the stress (load) is kept constant[4]. For small strains, the constant load and constant stress creep processes are the same[5]. Creep is appreciable at temperatures above 0.4 Tm, where Tm is the melting temperature. According to a typical representation of creep phenomenon in metals, well-known from literature, three different stages can be recognized and these are: primary, secondary and tertiary creep. Temperature and time dependence of a creep deformation process indicate that creep is a thermally activated process. Dislocation climb, vacancy diffusion and grain boundary sliding are usually numbered as mechanisms of creep[6]. The laboratory creep procedure is conducted at constant stress (load) and temperature, but components of machines in service hardly ever operate under constant conditions[7]. Also, low temperature service conditions represent an important challenge for steel today, especially steel plates. Low design temperatures require steel exhibiting sound fracture toughness behavior combined with high strength. Although much research has been carried out with different kinds of steel in question, they do not have the same characteristics. Some of the researches mentioned and published are listed in the following part of this paper. Some relative effects of various temperatures on the microstructure and mechanical properties of electron beam welds of X17CrNi16-2

132 Vol.29 No.1 Brnic J et al: Signi cance of Experimental Data in the Design of Structures...

martensitic stainless steel were studied[8]. The results of nitrogen plasma immersion ion implantation into differently preheated steel (martensite and ferrite structure of different steel, including X17CrNi16-2 , X20Cr13) are reported[9]. An interesting study based on wear behavior of martensitic stainless steel was carried out in Ref.[10]. As found in this investigation, some martensitic stainless steel samples such as X17CrNi16-2, X20Cr13 and others, were injected with nitrogen using plasma immersion ion implantation at different temperatures between 320 and 380 and at different pulse voltages. The formation of an expanded martensite layer was found after implantation for all samples with surface hardness up to 10.000 MPa. Wear was measured in a dry ball-on-disc con guration. Specific wear was reduced by factors of 2-10 to the same absolute level. Through an increase in the contact pressure, an increased wear rate was found, while on the other hand no in uence of velocity was observed. A study of difference in both corrosion and abrasion resistances between amorphous-nanocrystalline composite structured Ni-P deposits and microcrystalline structured Ni-P deposits is presented[11], where electroplating parameters affecting phosphorus content in Ni-P deposits (temperature, current density, pH, H3PO3 concentration and agitation rate) were analyzed in order to obtain amorphous-nanocrystalline composite structured Ni-P deposits on X17CrNi16-2 stainless steel. In Ref.[12], the slurry erosion of two coatings applied by oxy fuel powders and wire arc spraying processes onto sand-blasted AISI 304 steel was studied and the results were compared with those obtained with X17CrNi16-2 and ASTM A743 stainless steel, which are commonly used for hydraulic turbines and accessories. Sometimes it is interesting to make a comparison between the mechanical properties of the steel in question (X17CrNi16-2) and other kinds of steel, e g, high-strength low-alloy steel (HSLA), structural steel or steel which is commonly used in the can-making industry but also consider material behavior under similar environmental conditions. Some details relating to this matter can be found in Refs.[13- 17].

2 Material under consideration and experimental equipment

Material under consideration was 1.4057 steel (DIN/EN: X17CrNi16-2; AISI 431) with the following composition in mass (%): C (0.156), Si (0.496), Mn

(0.6749), Cr (15.9), Ni (1.42), Mo (0.234), Cu (0.0160), S (0.0228), P (0.0403), V (0.03859), Rest (81.0).

Because this is high yield strength steel, it is not readily cold worked; therefore it is not recommended for those operations. Under an annealed condition, this grade is relatively easily machined, but if hardened to above 30HRC machining becomes more difficult. This steel has the best corrosion resistance arnong all martensitic steel although it is lower than the common austenitic grades. It can be widely used in industry, especially in the aircraft industry. Typical applications include: nuts and bolts, pump shafts, propeller shafting, machine building industry, paper industry, aircraft fastener fittings, chemical process equipment, gears, etc.

The basic testing equipment for experimental investigations was the materials testing machine. For testing at low temperatures, a temperature chamber was used, while at elevated temperature a high temperature furnace and a high temperature extensometer were employed. Notch impact energy was determined by a Charpy impact pendulum machine.

The test specimens were taken from AISI 431 (X17CrNi16-2) steel rods and prepared according to the appropriate standard. Uniaxial tensile tests were performed according to ASTM: E8M-11 standard at room temperature and ASTM: E21-09 standard at elevated temperature, while those at low temperatures according to ISO 15579:2000(E) standard[18]. Testing procedures with reference to material creep behavior were carried out according to the ASTM: E139-11 standard. All of the ASTM standards mentioned are given in Ref.[19].

3 Results and discussion

3.1 Mechanical properties at low and elevated temperatures Engineering diagrams (stress-strain behavior)

of 1.4057 (AISI 431; X17CrNi16-2) steel at low temperatures are presented in Fig.1, while engineering diagrams at elevated temperatures are presented in Fig.2.

The effect of low and elevated temperatures on mechanical properties for 1.4057 (AISI 431; X17CrNi16-2) steel is presented in Fig.3.

The effect of elevated temperatures on specimens elongation (Ht) and reduction in area ( \) for 1.4057 (AISI 431; X17CrNi16-2) steel is exhibited in Fig.4.


3.2 Uniaxial short-time creep testsShort-time creep tests were performed under

selected environmental conditions.The appropriate creep responses are shown in

Figs.5-7.

3.3 Engineering calculation of fracture toughness based on Charpy V- notch impact energy A number of tests for determining different

material properties are performed. Based on the main purpose of structure during its service life, some selected properties such as ultimate tensile strength, hardness, modulus of elasticity, fracture toughness or any other, may be of crucial interests. However, two key mechanical properties are fracture toughness and yield strength. Fracture toughness (KIc), called plane strain fracture toughness is used to design


structure against fracture while yield strength (V0.2) is used to design structure against plastic deformation. Fracture mechanics, as a discipline underlying design against fracture, may be treated as a subject concerned with predicting the failure of a structural component containing crack-like defects[20]. Stress intensity factor (marked as SIF or K) is a parameter that describes stress distribution around the crack tip. Critical value of the SIF , designed as a minimum value of fracture toughness (KIc) has been introduced to define the nominal stress at which fracture takes place. A fracture toughness test can be used to measure the resistance of a material to crack extension[21]. However, this test may yield either a single value of fracture toughness or a resistance curve. Also, other fracture parameters may be considered. Fracture toughness standards prescribe procedures for obtaining (testing) certain fracture parameter or appropriate resistance curve[21,22]. Usually several specimen configurations are permitted under ASTM standard E 399 for KIc testing and these are, for example: the compact, SENB (single edge notched bend), arc-shaped, and disc-shaped specimens. The force value computed from the equation given in the standard mentioned is a valid KIc result only if all given validity requirements of the standard are met. The J-integral is usually used in a rate-independent quasi-static fracture analysis and can be related to the SIF if the material response is linear. Fracture toughness (KIc) is the most useful material property in the design against fracture, but there are also other tests that provide a fracture resistance measurement. Namely, measurements of KIc involve the use of large specimens which are difficult to excise from an operating structural component. An impact test widely used in ferrous metals and the plastics industry is one such test performed by the Charpy pendulum impact machine. On the other hand, notch acuity as well as temperatures used in the test do not have to be representative for conditions in which different types of steel are used. This means that the results of Charpy impact tests cannot be used directly to predict in-service behavior and failure characteristics, because the fracture mode depends not only on the properties of steel, but also on the parameters stated. Although the Charpy test is easy to perform and is a very useful test for assessing the quality of a product, it may be misleading to directly apply the results to real industrial applications. Namely, the energy of fracture depends on sample geometry, and many structures do not contain notches of the type used in Charpy tests. However, to avoid complication

in the standard test of fracture toughness measurement, some relationships between fracture toughness (KIc) and Charpy notch impact toughness (CVN) were proposed. One of them is presented and explained in[14]:

(1)

Through this equation, it is possible to determine the average value of KIc. The form of this equation is very similar to that in Ref.[22]. Use of Eq.(1) may have the advantage of assessing fracture toughness because parameters (E, CVN and Q) at selected temperature can be experimentally determined.

Eq.(2) includes: KIc (MPa ) - fracture toughness, E (MPa) - modulus of elasticity, (J/mm2) - impact toughness, and Q-Poissons ratio. Factor f is a factor whose value can be adopted, for example, according to the region of notch impact energy value. In general, fracture toughness is usually considered at room temperature. The impact toughness ( ) can be calculated as:

= K(U)/A or = K(V)/A = CVN/A (2)

In Eq.(2), U or V is a symbol for the type of notch used. The type of specimen notch depends largely on the characteristics of the material employed. In the present case, a 2 V notch was used.

Charpy V-notch impact energy (CVN) is expressed in (J), and it is experimentally obtained, while A (mm2) is a cross-sectional area of the Charpy impact specimen at the place of notch. For the Poisson ratio of this material, a value of Q= 0.3 was adopted and the cross-sectional area of the specimen was A= 80 mm2. At temperature of 20 the following average values for CVN and E were experimentally obtained:

K (V) = CVN = 55 J, E= 205 000 MPa

If an average value of f = 15 is adopted, according to Eq.(1) and Eq.(2), the following values were calculated:

According to correlation between CVN and KIc, given in Refs.[23,24], for an applicable region of CVN = (7- 68) J, the following formula is given:

KIc = 14.6 (CVN)1/2 (3)


Using Eq.(4), the following value for fracture toughness is calculated:

Also, according to equation[24, 25]:

KIc = 8.47 (CVN)0.63 (4)

which is assumed to be applicable to test data at all temperatures; the following value is calculated:

Sound consistency between the obtained values using Formulas (2), (4) and (5) can be observed.

Comparing Eq.(2) and Eq.(5), factor f can be expressed as follows:

(5)

If factor f is calculated using Eq.(5) with experimentally obtained CVN values at different temperatures, fracture toughness can be calculated. However, using Eq.(5), in Table 1, data related to fracture toughness are displayed. The corresponding curves of CVN energy and fracture toughness versus temperature are displayed in Fig.8.

In the literature, experimentally obtained data pertaining to the fracture toughness of the material under consideration (AISI 431) can not be found . The fracture toughness of AISI 431 steel, which is derived from the calculation based on the experimentally determined Charpy impact energy in this research, is 105.8 MPa . This data can be compared with the data related to the fracture toughness that can be found in

Ref. [26]. Namely, in the literature[26] it is specified as the value of the experimentally obtained fracture toughness for steel AISI 430, i e, for the steel of AISI 400 series. This steel contains slightly less carbon than steel AISI 431. In Ref.[26], for the fracture toughness at room temperature the value of 88 MPa is given. Taking into account that aforementioned steels (AISI 431 and AISI 430) are not completely the same, although they belong to the AISI 400 series, it can be said that calculated value for fracture toughness of AISI 431 steel, based on Charpy impact energy, can be considered quite reliable, because fracture toughness of both steels does not differ so much.

3.4 DiscussionAccording to stress versus temperature behavior

in Fig. 3, it can be observed that up to a temperature of 250 both ultimate tensile strength and 0.2 percent offset yield strength fall slightly with an increase of temperature. Also, in a temperature range between 300 and 550 these properties/strengths decrease quite rapidly. Elongations of steel at elevated temperatures during the first period of an increase of temperature, e g, up to 300 , do not exhibit abrupt change, while subsequently elongations increase rapidly. Observing mechanical properties at low temperatures, it can be seen that ultimate tensile strength rises slightly while the temperature decreases. At the same time, during a fall in temperature down to (-50) , 0.2 percent offset yield strength slightly rises and then decreases. This steel can withstand high temperature exposure quite well if stress levels are low enough. For example, at a temperature of 400 if the stress level does not exceed approximately


25% of 0.2 percent offset yield strength, creep strains in the short-time creep condition may be acceptable. Practically, the same can be said for a temperature of 500 . Also, if the temperature increases up to 600 and the stress level is kept quite low, e g, below 15% of 0.2 percent offset yield strength, creep strains are not high. In addition, Charpy V-notch impact energy was measured and notch impact toughness was calculated. According to the CVN data, using the proposed formulas, average values of fracture toughness were also calculated.

4 Conclusions

F o r e n g i n e e r i n g p r a c t i c e , i n t e r e s t i n g experimentally-obtained data regarding the behavior of AISI 431 (X17CrNi16-2) steel under different environmental conditions is presented. In these experimental investigations, the ultimate tensile strength and 0.2 percent offset yield strength at low and elevated temperatures were determined. Obtained results are presented in the form of engineering stress-strain diagrams. Temperature dependence of mechanical properties is also shown. Short-time creep behavior was considered and creep responses are displayed in the form of creep curves. As it can be seen tensile strength and 0.2 offset yield strength are of high levels at room temperature but with temperature increase they decrease rapidly. Regarding short-time creep behavior it can be said that this steel can not be treated as enough creep resistant in applications and service conditions where high temperature in combination with high level of stress arise, should be avoided. Finally, an assessment of fracture toughness using well known formula based on Charpy impact energy is made for certain temperature levels.

References[1] Bram tt B L. Effects of Composition, Processing, and Structures on

Properties of Irons and Steels, In: S. R. Lampman (Ed.), Materials Selection and Design[M]. OH: ASM International, 1997

[2] Boresi A P, Schmidt R J. Advanced Mechanics of Materials[M]. sixth ed. New York: John Wiley & Sons, 2003

[3] Collins A. Failure of Materials in Mechanical Design[M]. Second ed. New York: John Wiley & Sons, 1993

[4] Solecki R, Conant P R. Advanced Mechanics of Materials[M]. New York: Oxford University Press, 2003

[5] Findley W N, Lai J, Onaran S K. Creep and Relaxation of Nonlinear Viscoelastic Materials[M]. New York: Dover Publication, 1989

[6] Raghavan V. Materials Science and Engineering[M]. New Delhi: Prentice- Hall of India, 2004

[7] Timmins P F. Failure Control in Process Operations, In: S R Lampman Ed. Fatigue and Fracture[M]. OH: ASM International, 1997

[8] Rajasekhar A, Madhusudhan G R, Mohandas T, et al. Influence of

Austenitizing Temperature on Microstructure and Mechanical

Properties of AISI 431 Martensitic Stainless Steel Electron Beam

Welds [J]. Materials & Design, 2009, 30 (5): 1 612-1 624

[9] Manova D, Mndl S, Neumann H, et al. Influence of Annealing

Conditions on Ion Nitriding of Martensitic Stainless Steel [J]. Surface

and Coatings Technology, 2006, 200 (22-23): 6 563-6 567

[10] Manova D, Mndl S, Neumann H, et al. Wear Behaviour of Martensitic

Stainless Steel after PIII Surface Treatment[J]. Surface and Coatings

Technology, 2005, 200 (1-4): 137-140

[11] Yuan X, Sun D, Yu H, et al. Preparation of Amorphous-nanocrystalline

Composite Structured Ni-P Electrodeposits[J]. Surface and Coatings

Technology, 2007, 202 (2): 294-300

[12] Santa J F, Baena J C, Toro A. Slurry Erosion of Thermal Spray Coatings

and Stainless Steels for Hydraulic Machinery[J]. Wear, 2007: 263

(1-6): 258-264

[13] Brnic J, Turkalj G, Canadija M, et al. Creep Behavior of High-strength

Low-alloy Steel at Elevated Temperatures[J]. Mat. Sci. Eng. A, 2009,

499 (1-2): 23 - 27

[14] Brnic J, Turkalj G, Canadija M, et al. 50CrMo4 Steel-Determination of

Mechanical Properties at Lowered and Elevated Temperatures, Creep

Behavior and Fracture Toughness Calculation[J]. J. of Engineering

Materials and Technology.-Trans. ASME, 2010, 132 (2): 021 004

[15] Pepelnjak T, Barisic B. Computer-assisted Engineering Determination

of the Formability Limit for Thin Sheet Metals by a Modified

Marciniak Method[J]. Journal of Strain Analysis for Engineering

Design, 2009, 44 (6): 459-472

[16] Brnic J, Turkalj G, Canadija M. Optimal Design Procedure Based on

Viscoplastic Material Behaviour[J]. Acta Metallurgica Sinica, 2000,

13 (2): 587-592

[17] Brnic J, Niu J, G Turkalj G, et al. Behavior of HSLA A709 Steel at

Different Environmental Conditions[J]. Journal of Wuhan University

of Technology-Mater. Sci. Ed., 2010, 25 (6): 897-902

[18] International Standard. Metalic Materials-Tensile Testing at Low

Temperature[S]. ISO 15579:2000(E), 2000

[19] ASTM International. Annual Book of ASTM Standards, Metal

Test Methods and Analytical Procedures[M]. Baltimore: ASTM

International, 2012

[20] Zhang L. Failure Assessment of Thin-walled Structures with Particular

Reference to Pipelines[M]. Southampton: WIT Press, 2010

[21] Anderson T L. Fracture Mechanics[M]. New York: CRC Press, 1995

[22] Courtney T H. Fundamental Structure-property Relationships in

Engineering Materials, In S. R. Lampman Ed. Materials Selection and

Design[M].OH: ASM International, 1997

[23] Shekhter A, Kim S, Carr D G, et al. Assesment of Temper Embrittlement

in an Ex-service 1Cr-1Mo-0.25V Power Generating Rotor by Charpy

V-Notch Testing, KIc Fracture Toughness and Small Punch Test[J]. Int.

Journal of Pressure Vessels and Piping, 2002, 79 (8-10): 611-615

[24] Roberts R, Newton C. Interpretive Report on Small Scale Test

Correlations with KIc Data[C]. Welding Research Council Bulletins,

1981

[25] Y Chao, J D Ward, R G Sands. Charpy Impact Energy, Fracture

Toughness and Ductile-brittle Transition Temperature of Dual-phase

590 Steel[J]. Materials & Design, 2007, 28(2): 551-557

[26] Farahmand B, Bockrath G, Glassco J. Fatigue and Fracture Mechanics

of High Risk Parts[M]. New York: International Thomson Publishing,

1997

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Signicance of Experimental Data in the Design