一种基于激光雷达点云的高架边墙提取方法

A low alloy sintered steel contains at least 0.15 wt.% but less than 0.8 wt.% C. The matrix is tempered martensite contg. prior austenite crystal grains with a mean grain size of not more than 15 microns. The matrix has pores, non-metallic inclusions of max. dia. not larger than 50 microns, and a density of at least 96% of the theoretical density.

The steel is mfd. by: (i) treating raw material powder contg. at least one or atomised Fe or Fe alloy powder, in an inert atmos. of air, with a dry mill to introduce dislocations into the powder and pulverise non-metallic inclusions; (ii) softening/annealing the treated powder; (iii) adding and mixing the C; (iv) cold-forming the power to obtains a compact; (v) densifying the compact by sintering or hot plastic working; and (vi) heat treating the compact.

At least one of an oxide, carbide or nitride, with a mean particle size of not more than 0.5 microns, has at most a low solid solubility in the austenite phase, and is homogeneously dispersed in the matrix. The particles (pref. alumina) are added to the raw material powder in an amt. of 0.5-5 vol.% prior to treatment in a dry mill. The steel contains (wt.%): 10-300 ppm B, 0.05-3 of at least one of Nb, V, Ti, W and Al (added prior to dry milling) and 0.5-3 Cr, 0.1-1.5 Mo, 0.2-1.6 Mn, 0.5-3 Mi and 0.1-1.5 Mo. Step (ii) is carried out in a vacuum of non-oxidising atmos. at 600-1000 deg.C. Ferroboron powder is then added.

USE/ADVANTAGE -The steel is used in the mfr. of structural parts for machines, such as gears or a bearing race. The steel has excellent fatigue strength and toughness.

In an example, an Fe alloy powder (contg. 1.8 wt.% Fe, ).5 wt.% Ni, Mo) was mixed with 5 vol.% alumina powder of mean particle size 0.05 microns. The powder mixt. was treated in a dry mill under Ar for 40 hrs. The material was then annealed/softened under N2 at 800 deg.C for 1 hr., mixed with graphite powder, cold-formed, sintered in N2 at 1150 deg.C for 1 hr. and forged to produce a real:theoretical density ratio of at least 0.99. The forged body was carburised at 910 deg.C, held at 850 deg.C. quenched in oil and tempered at 200 deg.C for 90 mins. On testing, the resulting steel has a prior austenite grains size of 2.5 microns, a transverse rupture strength of 342 kg per mm2, an impact value of 5.9 kgf.m per cm2 and a fatigue strength of 120 kg per mm2.