Lead-free free-cutting beryllium copper alloy

Abstract

There is provided a lead-free free-cutting beryllium copper alloy consisting of from 1.80% to 2.10% by weight of Be, from 0.10% to 3.00% by weight of Si, from 0.20% to 0.40% by weight of Co, from 0% to 0.10% by weight of Fe, from 0% to 0.10% by weight of Ni, and the balance being Cu and inevitable impurities, wherein the beryllium copper alloy includes a matrix phase being an α phase, a Si-rich phase being a κ phase rich in Si, and Co—Be—Si intermetallic compound grains containing Co, Be, and Si, and optionally Fe and/or Ni.

What is claimed is: 
     
         1 . A lead-free free-cutting beryllium copper alloy, consisting of:
 from 1.80% to 2.10% by weight of Be;   from 0.10% to 3.00% by weight of Si;   from 0.20% to 0.40% by weight of Co;   from 0% to 0.10% by weight of Fe;   from 0% to 0.10% by weight of Ni; and   the balance being Cu and inevitable impurities,   wherein the beryllium copper alloy has:   a matrix phase being an α phase,   a Si-rich phase being a κ phase rich in Si, and   Co—Be—Si intermetallic compound grains containing Co, Be, and Si, and optionally Fe and/or Ni.   
     
     
         2 . The lead-free free-cutting beryllium copper alloy according to  claim 1 , wherein the Co—Be—Si intermetallic compound grains exhibit a hardness from 1.0 to 12.0 GPa as measured by a nanoindentation test in accordance with ISO14577. 
     
     
         3 . The lead-free free-cutting beryllium copper alloy according to  claim 1 , wherein the number of the Co—Be—Si intermetallic compound grains present at a cross section of the lead-free free-cutting beryllium copper alloy is 320 or less per unit area of 1 mm 2 . 
     
     
         4 . The lead-free free-cutting beryllium copper alloy according to  claim 1 , wherein when a cross section of the lead-free free-cutting beryllium copper alloy is observed, the Co—Be—Si intermetallic compound grains have a cross-sectional area from 0.3 to 70 μm 2  per grain. 
     
     
         5 . The lead-free free-cutting beryllium copper alloy according to  claim 1 , wherein when a cross section of swarf generated by cutting the lead-free free-cutting beryllium copper alloy is observed along a longitudinal direction, the cross section of the swarf has a sheared profile with zigzag-shaped unevenness that satisfies a relationship 1.10<h 2 /h 1 <6.60, wherein h 1  represents the average of distances between recesses in the zigzag-shaped unevenness, and h 2  represents the average of heights of protrusions in the unevenness. 
     
     
         6 . The lead-free free-cutting beryllium copper alloy according to  claim 1 , wherein in a phase map of 75 μm×75 μm field of view obtained by electron beam backscatter diffraction (EBSD) analysis of a cross section of the lead-free free-cutting beryllium copper alloy, the percentage of area S BCC  of BCC regions identified as body-centered cubic (BCC) lattices relative to the sum of area S FCC  of FCC regions identified as face-centered cubic (FCC) lattices and area S BCC , that is, 100×S BCC /(S FCC +S BCC ), is 5% or more.