Experimental Study Of High Frequency Micro-forging On Laser Hardening Layer Of45Steel

Laser surface hardening technology is a main means of surface strengtheningtechnology with high-energy density. In certain case it has some special characteristicswhich the traditional surface strengthening technology or other high energy densitysurface strengthening technology cannot or do not have, which makes the laser surfacehardening technology occupy a certain seat in surface hardening field. It has importantapplications in aviation, aerospace, machinery, energy and other fields. It has a notableeffect especially for some components with demand of high abrasion resistance, smallthermal deformation.Using the high frequency micro forging technology to treat laser hardened layer of45steel, the mechanical properties of45steel surfaces was further improved. Ultrasonicfrequency type forging mechanism used in this paper is to produce compressive plasticdeformation on the surface layer of the metal surface by high frequency forging punch;the high-density strain energy introduced by ultrasonic impact energy producedbeneficial compressive stress on the surface layer of the material. Under the treatment ofhigh energy and frequency shock the temperature of metal surface rises quickly anddecreases quickly, so that the surface metal organization changed, grain refined, surfacehardness and wear resistance performance were improved.This paper did some laser quenching experiments on45steel and selected a group ofsuitable laser quenching parameters of45steel. Then laser quenched45steel was forgedby high frequency micro-forging mechanism. Organizational changes before and afterforging were observed using SEM and metallographic microscope. Mechanicalproperties of45steel before and after forging were tested by micro hardness meter, Rockwell hardness, Block-on-Ring Wear test machine. The main reason for themicrostructure and mechanical properties change of45steel laser hardened layer causedby high frequency micro forging was analyzed. the mechanical properties changes in thecutting edge treated by high frequency micro forging processing was studied. Specificresults are listed as follows:1、the hardness on laser hardened surface of45steel changes obviously before andafter ultrasonic frequency micro forging processing, namely micro hardness of the45steel surface before and after micro-forging are855.7HV0.2and953.2HV0.2respectively，Rockwell hardness before and after micro-forging are57.48HRC and62.8HRCrespectively. It shows that the hardness and Rockwell hardness were increased by11.4%and9.26%respectively. After micro forging process, surface hardness influence depth of45steel is about0.15mm,and when the distance is farther farther away from the surface,micro forging effect is smaller and smaller.2、SEM photo of45steel changes obviously before and after micro forging. Aftermicro forging severe plastic deformation formed in the45steel quench zone surface,grains were forged into pieces and became smaller and refined.3、Abrasion performance of45steel laser hardened layer changes obviously before andafter micro forging. After micro forging the wear volume and quality reduces by about17.8%and14.6%respectively. It shows that after micro forging wear resistance of45steel increases obviously. After micro forging sample surface wear trace is not obvious,the distance between the grindings is tiny, the surface has no obvious furrow, grinding istinier than that before micro forging.4、After micro-forging the surface hardness of cutting edge surface was increased by23.4%. The metallographic structure of the surface changes obviously, original structurecharacteristics in sheet shape disappears, organizations become finer.