Carbon steels have wide range of mechanical properties in heat treated and surface treated i.e surface hardening, induction hardening, normalize, hardening.
Effect of Heat Treatment on Microstructural evolution and Mechanical Properties of C45 and Modified grades-C45-Mn & C45-Mn-Cr. 1 1 1 1 2 Authors: Khaqan Ali Khan , Qamar Hayat , Ibrar Ahmed , Farooq Iftikhar , Zafar Abbas 1
Pakistan Institute of Technology for Minerals and Advanced Engineering Materials (PITMAEM), PCSIR, Lahore 2
Institute of Advanced Materials, Bahauddin Zakariya University, Multan Abstract
Carbon steels have wide range of mechanical properties in heat treated and surface treated i.e surface hardening, induction hardening, normalize, hardening and tempering conditions depending upon carbon content. Modification of carbon steels are also used specially by adding Cr and Mn exceeding in amount form SAE/AISI standards. In this study effect of Cr and Cr-Mn on C45 Steel is examined after performing heat treatment including hardening in water and Oil followed by tempering. Microstructural examination was done to evaluate phase transformation. Mechanical testing including Tensile, hardness and impact tests were performed to compare C45 properties with modified grads. Introduction
Carbon steels are extensively used in structural, oil & gas and automotive applications. This family includes low, medium and high carbon steels and out medium carbon C45 is most commonly used grade because of its good mechanical properties and weldability. It is also heat treatable and respond to quenching thus it can be used in for several automotive parts in quenched and tempered and even in induction hardening condition. In oil quenching and tempered state, it is known that ferrite content appears on grain boundaries of second phase which drastically effect mechanical properties and also reduces its machinability. To reduce the ferrite content and to achieve good combination of mechanical properties and machinability several deviations from stranded C45 steels are used. Materials & Method Samples of C45, Modified with Mn and Cr-Mn. Spark emission Spectroscopy was used for Chemical compositional analysis of these three alloys presented in hot rolled condition with diameter 40mm and given designation A, B and C respectively. As received material is cut in cubical (10*10*30 mm3) form by using precision diamond cutter. Total 09 samples were taken to perform heat treatment and metallographic examination. Separate samples were produced as per ASTM standards with same heat treatment and designation as mentioned above for mechanical testing. ASTM A370 Standard was used for performing Tensile testing and 1000KN Shamazdu UTM machine was used for this purpose. Olympus microscope equipped with DP21 Image analysis software was used for ASTM grain size measurement. Heated Treated samples was also observed by using same microscope after polishing (320 to 2000) and grinding (6 µm and 1 µm). Samples were etched by 4% Nital solution (96% ethanol+ 4% Nitric Acid) for microstructural examination.
Sample I.D
%C
%Si
%S
%P
%Mn
%Cr
%Cu
%Ni
%Mo
Standard
0.43~0.50
0.15~0.35
0.05max
0.03max
0.6~0.9
-
-
-
-
A
0.45
0.30
0.008
0.0025
0.76
0.07
0.014
0.08
0.02
B
0.43
0.17
0.008
0.012
1.12
0.082
0.021
0.002
0.005
C
0.46
0.22
0.015
0.018
1.1
0..79
0.02
0.004
0.007
Results and Discussion Mechanical Properties Process
Sample I.D
Tensile (MPa)
Hardness (HBW)
Impact Energy (J)
As Rolled
A
620
211
143.178
Oil Quenching & Tempering
A
760
257
183.456
Water Quenching & Tempering
A
857
421
111.916
As Rolled
B
638
235
154.448
Oil Quenching & Tempering
B
788
278
195.412
Water Quenching & Tempering
B
907
466
107.604
As Rolled
C
667
248
160.132
Oil Quenching & Tempering
C
810
293
204.428
Water Quenching & Tempering
C
938
311
120.442
Conclusion 1. Mn content increase the hardenability of the C45 Steel, it also reduces the ferrite content on grain boundaries during oil quenching thus mechanical properties including hardness, tensile and impact goes up as compare to C45 Steel. Mn content also improves the machinability upto some extent. 2. Mn and Cr when added reduce ferrite content on grain boundaries and supports martensitic transformation. Only 7-10% ferritic contact is observed on grain boundaries and thus sample C has good tensile strength, hardness and impact along with much improved machinability.
