Research of laser transformation hardening on mild steel

ZHANG Pei-lei; DING Min; YAO Shun; YAO Cheng-wu

doi:10.3969/j.issn.1001-3806.2009.06.008

The effect of laser transformation hardening on the surface property and microstructure of mild steel 10CrNiMo under different laser power and cooling conditions was studied.A hardened layer on the surface of the mild steel was obtained whose microhardness is 100HV～150HV higher than that of the original mild steel The microstructure of laser processed zone was observed with a metallographic microscope and the hardness of laser processed layer was measured with a microhardness tester.The results showed that the quench zone consisted of martensite,retained sorbite,troostite,tempered sorbite and that the microstrcture in the lap zone was martensite and some sorbites locating in the middle of martensite.Because of the lower carbon content of steel 10CrNiMo and different carbon diffusion coefficient,the highest hardness did not appear on the surface but in the subsurface.In the softened zone,because the martensite produced by the first laser scanning was tempered by the second laser beam,the carbon in the martensite separates and changes into temper sorbite.Microhardness of lap zone declined due to the temper of second laser scanning.Laser transformation hardening can improve the surface hardness 100HV～150HV higher and keep good tenacity.Furthermore,laser cladding can be taken to increase the hardness more evidently.

Research of laser transformation hardening on mild steel

Corresponding author: YAO Shun, ys@sjtu.edu.en;

1. Shanghai Key Laboratory of Material Laser Processing and Modification, Shanghai Jiaotong University, Shanghai 200240, China

Received Date: 2008-09-07

Accepted Date: 2008-11-26

Available Online: 2009-12-25

Abstract: The effect of laser transformation hardening on the surface property and microstructure of mild steel 10CrNiMo under different laser power and cooling conditions was studied.A hardened layer on the surface of the mild steel was obtained whose microhardness is 100HV～150HV higher than that of the original mild steel The microstructure of laser processed zone was observed with a metallographic microscope and the hardness of laser processed layer was measured with a microhardness tester.The results showed that the quench zone consisted of martensite,retained sorbite,troostite,tempered sorbite and that the microstrcture in the lap zone was martensite and some sorbites locating in the middle of martensite.Because of the lower carbon content of steel 10CrNiMo and different carbon diffusion coefficient,the highest hardness did not appear on the surface but in the subsurface.In the softened zone,because the martensite produced by the first laser scanning was tempered by the second laser beam,the carbon in the martensite separates and changes into temper sorbite.Microhardness of lap zone declined due to the temper of second laser scanning.Laser transformation hardening can improve the surface hardness 100HV～150HV higher and keep good tenacity.Furthermore,laser cladding can be taken to increase the hardness more evidently.

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Reference (8)

[1]	ZHANG F J,BU D X,ZHANG G D,et al.Ultra-narrow gap gas-shield metal arc welding of 980 steel[J].Electric Welding Machine,2006(5):51-54(in Chinese).
[2]	LI T D,WANG Y,HE Q K,et al.Study on microstructure and performance of 45 steel treated by malti-time laser transformation hardening[J].China Surface Engineering,2007,20(2):33-37(in Chinese).
[3]	CHAO M J,DU Y D,LIANG E J,et al.Investigation of laser surface hardening for mould-cutting roller[J].Laser Technology,2003,27(6):500-503(in Chinese).
[4]	XU Z W,HUANG Zh,RU A,et al.Law of microstructural formation of low carbon steel in laser melting process and heating transformation of the melted microstructure[J].Heat Treatment of Metals,2003,28(10):22-25(in Chinese).
[5]	MA K,YANG Y L,WANG Ch Sh,et al.Effect of laser hardening technical parameters on hardened depth of 40Cr steel[J].Laser Technology,2002,26(4):262-263(in Chinese).
[6]	WU G,SONG G M,HUANG W J.Influence of laser processing parameters on the case-depth and the hardness[J].Laser Technology,2007,31(4):163-165(in Chinese)
[7]	LI J Ch.Research on optimization of controlling of laser heat treatment[M].Beijing:Metallurgical Industry Press,1995:155-160(in Chinese)
[8]	MIOKOVIC T,SCHULZE V,LOHE D,et al.Influence of heating rate,cooling rate and number of pulses on the microstructure of AISI 4140 after short-time-hardening[J].International Journal of Materals Product Technology,2005,24(1/4):207-230.

Research of laser transformation hardening on mild steel

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